A known printing system comprises a print station and a plasma generating device. Said plasma generating device is provided for providing plasma to a print substrate. Said print station is provided for applying an image on the print substrate after the plasma generating device has treated the print substrate by the plasma. The plasma generating device comprises a plasma electrode and a counter electrode having a plasma gap arranged in between them. The plasma is generated in operation of the plasma generating device inside the plasma gap between the plasma electrode and the counter electrode. Said plasma is used to chemically modify the surface of the print substrate. For example it is generally known that materials such as plastics, cloth, and paper may be passed through the plasma gap in order to change the surface energy of the material as is known from, for example, FR2578176 and GB925354.
A uniform plasma throughout the plasma gap is demanded to obtain a uniform surface energy of the print substrate. It is known that the distance of the plasma gap between the plasma electrode and the counter electrode is preferably uniform in order to obtain said uniform plasma.
In an example of the application of plasma on a web based print substrate the counter electrode is a cylindrical roller having a peripheral surface. In operation the peripheral surface of the cylindrical roller is rotated along the stationary plasma electrode. The plasma electrode is arranged extending in the axial direction of the cylindrical roller.
In another example of the application of plasma on a cut sheet print substrate the counter electrode comprises a stationary flat surface along the plasma gap. In any of these examples the distance of the plasma gap between the plasma electrode and the counter electrode is adjusted prior to operating the plasma generating device by measuring the distance in the plasma gap and if necessary adjusting the position of one end or both ends of the plasma electrode with respect to the counter electrode. The adjustment of the plasma gap is time consuming and measurements need to be carried out along a lateral direction of the plasma gap.
Even more in case the plasma generating device comprises more than one plasma electrode arranged with respect to the common counter electrode, each of the corresponding plasma gaps with respect to the counter electrode needs to be measured independently and if necessary the position of each of the corresponding plasma electrode needs to be adjusted.